Water-borne fluoroelastomer coatings and cured films therefrom

ABSTRACT

A water-borne fluoroelastomer composition comprising an aqueous dispersion of a fluoroelastomer polymer, from about 2 to about 30 parts by weight per one hundred parts by weight of polymer of a curative system, said curative system having been formed by blending from about 6 to about 94 parts by weight of a stabilized siloxane and from about 94 to about 6 parts by weight of a non-stabilized silane, where said stabilized siloxane and said non-stabilized silane total about one hundred parts by weight of the curative system, from 0 to about 40 parts by weight of an additive filler per one hundred parts by weight of polymer, and sufficient water to provide a composition having a solids content of from about 10 to about 80 percent by weight of the total composition.

TECHNICAL FIELD

The present invention is generally directed toward fluoroelastomercoating compositions and coatings and cured films therefrom. Moreparticularly, the present invention is directed toward water-bornefluoroelastomer compositions having a technologically useful pot life,and that give rise to films having improved physical propertiesincluding adhesion and strength. Specifically, the water-bornefluoroelastomer coatings of the present invention contain a novelcurative system that includes a blend of a stabilized siloxane curativewith a non-stabilized silane curative.

BACKGROUND OF THE INVENTION

Fluoroelastomer coating compositions are well known. They typicallycomprise copolymers of vinylidene fluoride and hexafluoropropylene orterpolymers of vinylidene fluoride, hexafluoropropylene andtetrafluoroethylene.

Fluoroelastomers are well known for their heat, weather, solvent andchemical resistance. Furthermore, cured fluoroelastomer films typicallyexhibit good mechanical properties and adhere to a variety of surfaces.As a result of these properties, fluoroelastomer coating compositionsare applied to protect a variety of surfaces including metals, plastics,rubbers, concrete, glass and the like.

Heretofore in the art, fluoroelastomer coating compositions have beenapplied by using organic solvent systems. Typical solvent systemsemployed ketones or ethers. Such solvents, however, are hazardous to useinasmuch as they are flammable, toxic, and volatile. Moreover, growingenvironmental concern over the use of such volatile organic compoundsrestricts the use of such compounds in various areas of the country.Finally, the pot life of the fluoroelastomer coating compositionsemploying such solvents is generally only a few hours. Pot life, as itwill be used herein, refers to the time required for the fluoroelastomercoating composition to begin gelation.

Water-borne fluoroelastomer coating compositions are also known. Forexample, DuPont de Nemours Company, of Wilmington, Delaware teachesaqueous dispersions of their fluoroelastomer, VITON®, with a polyaminecuring agent. The pot life of such dispersions, however, is relativelyshort, generally only 2 to 5 days. Ausimont U.S.A. also teaches aqueousdispersions employing their fluoroelastomer, TECNOFLON®, with aliphaticamines as curing agents. As with the dispersions taught by DuPont, thoseemploying aliphatic amines also have a relatively short pot life, on theorder of only 3 to 5 days.

U.S. Pat. No. 4,399,553 also teaches a water based fluoroelastomercoating composition containing partially or completely hydrolyzedaminosilane compounds, with or without additional amine compounds, ascuring agents. These aqueous dispersions are taught to have a pot lifeof up to one month at 25° C.

Thus, although water based fluoroelastomer coating compositions areknown, a need still exists for a water based fluoroelastomer coatingcomposition having improved pot life, excellent stability, and whichproduces cured films with excellent adhesion to a wide variety ofsubstrates.

SUMMARY OF INVENTION

It is therefore an object of the present invention to provide afluoroelastomer coating composition as well as coatings and cured filmtherefrom.

It is another object of the present invention to provide afluoroelastomer coating composition having a technologically useful potlife.

It is yet another object of the present invention to provide cured filmsof fluoroelastomer coating compositions having improved adhesionstrength.

It is still another object of the present invention to providefluoroelastomer coating compositions that are essentially devoid ofvolatile organic compounds.

Is another object of the present invention to provide cured films offluoroelastomer coatings that exhibit good abrasion resistance.

It is yet another object of the present invention to providefluoroelastomer coatings and cured films that have improved resistanceagainst a wide variety of solvents and chemicals once cured.

It is still another object of the present invention to provide afluoroelastomer coating composition that does not contain acid acceptorscommonly used in fluoroelastomer compositions.

At least one or more of the foregoing objects, together with theadvantages thereof over the known art relating to water-bornefluoroelastomer coating compositions and coatings and cured filmstherefrom, shall become apparent from the specification that follows,and are accomplished by the invention as hereinafter described andclaimed.

In general the present invention provides a water-borne fluoroelastomercomposition comprising an aqueous dispersion of a fluoroelastomerpolymer, from about 2 to about 30 parts by weight per one hundred partsby weight of polymer of a curative system, said curative system havingbeen formed by blending from about 6 to about 94 parts by weight of astabilized siloxane and from about 94 to about 6 parts by weight of anon-stabilized silane, where said stabilized siloxane and saidnon-stabilized silane total about one hundred parts by weight of thecurative system, from 0 to about 40 parts by weight of an additivefiller per one hundred parts by weight of polymer, and sufficient waterto provide a composition having a solids content of from about 10 toabout 80 percent by weight of the total composition.

The present invention also includes a method for a fluoroelastomer filmprepared by a process comprising the step of curing a water-bornefluoroelastomer composition of matter with a curative system thatincludes a mixture of a stabilized siloxane and a non-stabilized silane.

The present invention also includes a method for a fluoroelastomer filmprepared by applying the composition to a substrate, wherein thefluoroelastomer composition includes an aqueous dispersion offluoroelastomer polymer, from about 2 to about 30 parts by weight perone hundred parts by weight of polymer of a curative system, saidcurative system having been formed by blending from about 6 to about 94parts by weight of a stabilized siloxane and from about 94 to about 6parts by weight of a non-stabilized silane, where said stabilizedsiloxane and said non-stabilized silane total about one hundred parts byweight of the curative system, from 0 to about 40 parts by weight of anadditive filler per one hundred parts by weight of polymer, andsufficient water to provide a composition having a solids content offrom about 10 to about 80 percent by weight of the total composition,and curing the applied composition.

The present invention also includes a method for a water-bornefluoroelastomer composition comprising an aqueous dispersion of afluoroelastomer polymer, from about 2 to about 30 parts by weight perone hundred parts by weight of polymer of a curative system, saidcurative system comprising a mixture of a stabilized siloxane andnon-stabilized silane, from 0 to about 40 parts by weight of an additivefiller per one hundred parts by weight of polymer, and sufficient waterto provide a composition having a solids content of from about 10 toabout 80 percent by weight of the total composition.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

It has now been discovered that improved fluoroelastomer coating andcured fluoroelastomer films can be obtained from water-bornefluoroelastomer coating compositions containing a novel curative system.By water-borne, it is meant that the compositions are based on aqueousdispersions or latices of fluoroelastomer polymers. More specifically,it has been found that the use of the novel curative system of thisinvention provides for fluoroelastomer compositions having a useful potlife that yields coatings and cured films having improved propertiesover those coatings and films prepared from compositions that do notemploy the novel curative. Accordingly, the present invention isgenerally directed toward water-borne fluoroelastomer compositions thatinclude fluoroelastomer polymers, a novel curative system, and optionalfillers, as well as coatings and cured films prepared from thiswater-borne fluoroelastomer composition.

Fluoroelastomers that can be cured by the novel curative system of thepresent invention include any of those obtained from copolymerizablefluorine containing monomers, but preferably include copolymers ofvinylidene fluoride, and hexafluoropropylene, or terpolymers ofvinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene. Otherexamples of fluoroelastomers include those modified with monomers thatprovide enhanced properties, e.g., copolymerization withperfluoro(methylvinylether) to improve low temperature performance.Mixtures of the above fluoroelastomers may also be employed. Forpurposes of this specification, the term fluoroelastomer will be used torefer to compositions of fluoroelastomers including mixtures of thesefluoroelastomers.

The novel curative system of this invention includes a mixture of awater-soluble, stabilized amino-siloxane curative and a non-stabilizedsilane curative. For purposes of this specification, these curatives maysimply be referred to as the stabilized and non-stabilized curatives,respectively, or they may be referred to stabilized siloxanes andnon-stabilized silanes, respectively. Preferably, the curative systemwill include from about 6 to about 94 parts by weight stabilizedcurative and from about 94 to about 6 parts by weight non-stabilizedcurative, wherein the stabilized and non-stabilized curative total about100 parts by weight. Even more preferably, the curative system willinclude from about 40 to about 60 parts by weight stabilized curativeand from about 33 to about 67 parts by weight non-stabilized curative,wherein the stabilized and non-stabilized curative total about 100 partsby weight. It should be appreciated that the foregoing parts by weightare based upon the weight of solution of each curative. The siloxane isan aqueous solution that contains between about 20 to about 30 percentby weight solids. The silane, on the other hand, is typically a liquidat room temperature and contains essentially no water. Usually, theliquid silane contains greater than about 90 percent by weight activeingredients.

With regard to the first component of the mixture within the curativesystem of this invention, the water-soluble, stabilized amino-siloxanecuratives include oligomeric siloxanes where the degree ofpolymerization of the oligomeric siloxane is essentially limited. Byessentially limited, it is meant that the average degree ofoligomerization of the siloxanes within an aqueous solution is aboutthree or less.

It should be appreciated that silanes readily undergo hydrolysis inwater to produce silanols. Silanols will self condense to form siloxaneoligomers. This self-condensation continues beyond the soluble dimer andtrimer to yield insoluble tetramers and higher, including branched andcyclic species. It is believed that these insoluble compoundsdeleteriously affect the ability of the siloxane oligomer to curefluoroelastomers in water-borne coating compositions.

Without wishing to be bound by any particular theory, it is neverthelessbelieved that the water-soluble, stabilized amino-siloxane curativesemployed in the present invention are stabilized--and thus prohibitedfrom further polymerization or self-condensation--as a result of otherconstituents that are present in the aqueous solution containing thesiloxanes. For example, hydrolyzed alkoxysilanes that are inhibited fromfurther self-condensation by using an emulsifier are disclosed in U.S.Pat. No. 5,552,476. Also, European Published Application 675,128discloses stable, water-borne silane compounds.

As noted above, the water-soluble, stabilized amino-si loxane curativeis an oligomeric siloxane where the average degree of polymerization ofthe siloxanes is essentially limited to a trimer or less. Thisoligomeric trimer can be defined by the formula (I) ##STR1## where R¹,R², and R³ are the same or different and are selected from the groupconsisting of amino groups, organic moieties, and hydrogen, with theproviso that at least one of R¹, R² and R³ contain an amino group. Thefunctionality, size and/or configuration of each of R¹, R² and R³,individually or in combination, must be such that the oligomer issoluble, miscible or dispersable in water or aqueous mediums, whichhereinafter will be referred to as soluble or water soluble. Inasmuch asa multitude of amino-siloxanes can fall within the parameters set forthin formula (I), it should be appreciated that a mixture of thestabilized siloxanes, all generally defined by formula (I), can beemployed in the present invention. The skilled artisan will readilyappreciate that dimers according to formula I simply include thosecompounds that will include two silicon atoms as opposed to the threesilicon atoms shown in Formula I. And, it should be understood thatreference to water-soluble, stabilized amino-siloxane curatives or thosecompounds represented by the formula I will, for purposes of thisspecification, include all oligomeric siloxanes that are, on average, atrimer or less, and that are soluble in water.

The amino groups referred to above include primary and secondary aminogroups, as well as primary and secondary amine substituted organicmoieties. Reference to amino groups also includes polyamino groups,which are groups that include more than two amine nitrogens, and refersto those groups than include both primary amino and secondary aminogroups. Preferably, the amino groups are primary amine groups, primaryamine substituted organic moieties, or polyamino substituted organicmoieties.

Organic moieties refer to alkyls, alkenes and alkynes, which can bestraight or branched. It is contemplated that these moieties can also becyclic or aromatic.

It should further be understood that the organic moieties can includehetero atoms, such as oxygen or sulfur, so long as the presence of theseatoms does not have a deleterious affect on the oligomer or thecomposition of the present invention. Preferably, the organic moietiesare alkyls.

Regarding the proviso that at least one of R¹, R², and R³ contain anamino group, it is preferred that the amino-siloxane curative contain atleast two reactive amine functionalities so as to best achievecrosslinking of the fluoroelastomer monomers. In other words, it ispreferred that at least two of R¹, R² and R³ contain amino groups or atleast one of R¹, R² and R³ contain a polyamino group.

Certain examples of the substituents R¹, R², and R³ can be definedaccording to the following formula (II) ##STR2## wherein R⁴ is adivalent organic moiety as defined hereinabove, R⁵ is selected fromhydrogen and organic moieties as defined hereinabove; and n is 0 or 1.It is preferred that n is 1 and that R⁴ is an alkyl. It should beunderstood that where R¹, R², or R³ are hydrogen, formula (II) is notrepresentative. And, it should be understood that formula (II) is notrepresentative of substituents that contain more than one aminenitrogen, although these substituents are contemplated by thisinvention.

Those skilled in the art, without undue experimentation, can readilydetermine the maximum size and/or appropriate configuration ofsubstituents R¹, R², and R³ that is permissible without rendering theoligomer insoluble in aqueous media. It should be understood that thesize of the substituent refers to the number of carbon atoms therein.

Although the stabilized curatives of this invention are not limited toany particular size and/or molecular weight, it is believed that each ofR¹, R² and R³ can include up to about 6 carbon atoms without renderingthe molecule insoluble. The solubility of the curative, of course, willimprove with fewer carbon atoms, as well as with the addition ofsubstituents such as nitrogen and oxygen atoms. The amount of branchingwill also affect the solubility. Thus, the skilled artisan may be ableto synthesize larger molecules by adding other substituents and/orchanging the chemical structure of R¹, R² or R³. Furthermore, althoughthe size of any given substituent, e.g. R¹, can fluctuate based on thesize of the complementary substituent groups, e.g. R² and R³, it isbelieved, and thus preferred, that the oligomers employed in the presentinvention contain less than about 20 total carbon atoms, more preferablyless than 1 5 total carbon atoms, and even more preferably less than 12total carbon atoms. Again, it should be understood that largermolecules, so long as they are soluble, are contemplated.

A water-soluble, stabilized amino-siloxane that is useful in practicingthe present invention is the diamino siloxane sold by Sivento Inc. ofPiscataway, New Jersey, under the name HYDROSIL® 2776. It is believedthat this curative is hydrolyzed, terminated and stabilized, andtherefore is essentially limited to trimers or smaller. Another exampleof a stabilized siloxane is HYDROSIL® 2775, which is also sold bySivento. This is a triamino siloxane that is hydrolyzed, terminated andstabilized. It should be appreciated that although HYDROSIL® 2775 and2776 are examples of preferred embodiments, any stabilized amino orpolyamino siloxane meeting the above criteria can be used.

Turning now to the second component of the curative system of thisinvention, the non-stabilized curatives are preferably amino-silanecompounds. These amino silanes should contain at least one aminenitrogen, but can also include more than one amine nitrogen. Asdiscussed above, when placed in an aqueous environment, these silaneswill ultimately form siloxane oligomers and polymers.

These amino-silane compounds can be defined by the formula (III)##STR3## where R⁶ is an amino group, and R⁷, R⁸, and R⁹ areindependently selected from hydroxyl group, hydrogen, halogen, aminogroups, and organic moieties. Preferably, at least one of R⁷, R⁸, and R⁹are hydroxyl group. The amino groups and organic moieties refer to thesame groups that are more specifically defined above for R¹, R², and R³.Useful organic moieties include alkyl groups, hydroxy groups, alkoxygroups, substituted alkoxy groups, acyloxy groups, hydroxy alkoxygroups, epoxy groups, and the like. These groups preferably containbetween 1 and about 20 carbon atoms, more preferably between 1 and about12 carbon atoms, and even more preferably between 1 and about 5 carbonatoms.

Some examples of non-stabilized, amino-silane curatives known in the artinclude, without limitation:

γ-aminopropyltriethoxysilane,

N-β-aminoethyl-γ-aminopropyltrimethoxysilane,

γ-aminopropyltrimethoxysilane,

γ-(β-aminoethyl)aminopropylmethyldimethoxysilane,

trimethoxysilylpropyldiethylenetriamine,

The preferred amino-silanes include γ-aminopropyltriethoxysilane,N-β-aminoethyl-γ-aminopropyltrimethoxysilane, andTrimethoxysilylpropyldiethylenetriamine. These silanes are commerciallyavailable from several sources. For example,γ-aminopropyltriethoxysilane is available from Dow-Corning Corporationof Midland, Mich. under the tradename Z-601 1, from Sivento, Inc. ofPiscataway, N.J. under the tradename AMEO, and from Union CarbideCorporation of Danbury, Conn. under the tradename A-1100.N-β-aminoethyl-γ-aminopropyltrimethoxysilane is available fromDow-Corning under the tradename Z-6020, from Sivento under the tradenameTRIAMO, and from Union Carbide under the tradename A-1120.Trimethoxysilylpropyldiethylenetriamine is available from Sivento underthe tradename TRIAMO and from Union Carbide under the tradename A-1130.The foregoing list of commercially available products is by no meansexhaustive and those skilled in the art can readily obtain a number ofnon-stabilized silanes.

It has surprisingly been found that the combination of a stabilizedsiloxane and a non-stabilized silane yields a curative system that isimproved over curative systems that exclusively contain either astabilized siloxane or a non-stabilized silane. Indeed, thenon-stabilized silanes are ineffective as a curative in a water-bornesystem because they rapidly precipitate out of aqueous solution. And,the coatings and cured films prepared from compositions containing acurative of this invention are superior to those coatings and curedfilms prepared by using curative systems that simply include stabilizedsiloxanes. These advantages specifically include , but are not limitedto, the ability to cure within a reasonable amount of time at roomtemperature and improved adhesion to a number of substrates.

It is believed that stabilized siloxanes and non-stabilized silanes insomeway interact and form a product in aqueous solution. Potentially,this product could include a reaction product of the two curatives, aproduct formed by some forces of attraction, orsimplya mixed system thatis in equilibrium. Nonetheless, no such interaction may in fact exist.Because it is not desired to limit the invention to any particulartheory, the combination of the stabilized siloxane curative and thenon-stabilized silane will simply be referred to as a mixture, with theterm referring to a simple mixture as well as all products resultingfrom the interaction of the curative including simple forces ofattraction and chemical bonding. More generally, the stabilized siloxaneand the non-stabilized silane within aqueous solution will be referredto as the curative system.

With regard to the overall fluoroelastomer composition of thisinvention, the composition will generally include a fluoroelastomer,from about 2 to about 30 parts by weight of the curative system per onehundred parts fluoroelastomer (phr), and optionally from about 0 toabout 50 parts by weight filler phr. Preferably, the composition willinclude a fluoroelastomer, from about 6 to about 24 parts by weight ofthe curative system phr, and optionally from about 5 to about 40 partsby weight filler phr. More preferably, the composition will include afluoroelastomer, from about 12 to about 16 parts by weight of thecurative system phr, and optionally from about 10 to about 30 parts byweight filler phr.

The composition will also include water as a dispersing medium. Theamount of water should be sufficient so that the solids content of thecomposition, i.e., the fluoroelastomer, the curative system, theoptional filler and other additives, is from about 10 to about 80percent by weight of the entire composition including the water. Morepreferably, the solids content of the composition should be from about60 to about 73 percent by weight of the entire composition, and evenmore preferably from about 63 to about 70 percent by weight of theentire composition.

Useful fillers can include carbon black, mineral fillers (clays,synthetic silicates, whiting, barytes, and the like), color pigments(preferably inorganic and heat resistant), glass micro beads and short,chopped fibers, as well as materials to modify resistivity, such asmetal powders, graphite and the like. Other examples include thosematerials used as fillers in rubber, plastic and coating formulations.These fillers are well known and documented in the art. In essence, anymaterial that does not adversely affect the chemical and physicalperformance of the coating can be used as a filler. It should beappreciated that the presence or absence of any fillers and pigmentstypically does not affect the performance of the coating. Of course, thetotal amount of filler added will be limited by its effect on viscosity,film formation capabilities and other properties of the fluoroelastomercoating. Additional ingredients such as surfactants, viscosity modifiersand the like may be added if deemed necessary to control the liquidcoating properties. Although the preferred embodiments of the presentinvention include a filler, it should be understood that a compositionwithout filler falls within the scope of the present invention.

In preparing the compositions of this invention, it is preferred toprepare the curative system apart from the rest of the composition. Thisis preferably done by adding an appropriate amount of non-stabilizedsilane to the stabilized siloxane in water. This mixture may be referredto as the preblended curative system. This preblended curative system isthen blended with the fluoroelastomer as well as the optional fillersand other additives by using mixing techniques that are conventional inthe art. These techniques may include the use of a ball mill or othersuitable mixing equipment. Indeed, the conditions of mixing aredependent upon the coating composition ingredients and can be readilydetermined by those skilled in the art without undue experimentation.The coating composition mixture is preferably filtered to remove anyundispersed particles.

Alternatively, the curative system may be prepared in situ in certainsituations; that is, the stabilized siloxane and the non-stabilizedsilane may be separately added to the overall composition, i.e., latex,and subsequently mixed as discussed above. When adding the curativesdirectly to the fluorelastomer latex, it should be understood that thestabilized siloxane should be added first because the non-stabilizedsilane will undergo hydrolysis and self condense in the absence of thestabilized curative. One situation that has proved workable is theaddition of HYDROSIL® 2776 followed by the addition of A-1100 directlyto the latex.

The water-borne fluoroelastomer coating compositions of the presentinvention may be sprayed, dipped, brushed or applied in any similarfashion to form a film on the desired substrate, which can includemetal, rubber, plastic, concrete or other such surfaces. There are manyuses for the coatings or films of this invention that require films ofvarying thicknesses. Accordingly, the film thickness is chosen basedupon the application. Some applications include, without limitation,fabric coatings. These fabrics can then be made into suits or tarps thatcan be worn used to cover certain areas during toxic waste clean-up orin a variety of other situations where harmful chemicals that do notdeleteriously impact the fluoroelastomer coatings of this invention areencountered. The compositions of this invention can also be used to coatconcrete in secondary-containment areas. Further, the composition can beused to coat chemical storage tanks as well as the structures thatsupport these tanks. Still further, these compositions can be used tocoat objects, like rubber rolls or printing rolls, where there is a needto dissipate electrostatic charge or insulate certain articles fromelectric charge. In these applications, it is desirable to addconductive fillers including carbon black and various metals or metaloxides to the coating compositions and thereby form a conductive ordielectric coating. These coatings can also be used as RFI and EMIshielding. In fact, the coatings of this invention can be used in avariety electronic applications. Still further, the coatings of thisinvention can used to coat certain materials and components within fuelcells and batteries. And, it should be appreciated that based upon theadhesive properties of the coatings of this invention, there are avariety of articles, including articles made of rubber, steel, plastic,and the like that can be coated with the composition of this invention.This includes coating various articles that are used in many industries,including, without limitation, under-the-hood automotive, agriculture,petro and electrochemical, construction, electric, and electronics,marine, pulp and paper, aerospace, military, and many more.

Once a film is prepared, it may be cured by room or ambient temperatureor by heat curing . Where a thin film is prepared, such as a film thatis about 0.25 to about 15 mils thick, a cured film results at about roomtemperature within about 7 to about 10 days. Where a similar thin filmis prepared and subjected to heat in the range from about 60° C. toabout 200° C., a cured film can be produced within minutes, such asabout 5 minutes, or within a few hours, such as 4 hours, depending onthe heat. In a preferred embodiment, the uncured film or coating isfirst dried at ambient temperatures, or in an oven at 50° C. to about70° C., and then cured at higher temperatures, such as at about 100° C.,for about one hour.

In order to demonstrate the practice of the present invention, thefollowing examples have been prepared and tested as described in theGeneral Experimentation Section disclosed hereinbelow. The examplesshould not, however, be viewed as limiting the scope of the invention.The claims will serve to define the invention.

GENERAL EXPERIMENTATION EXPERIMENT I

Thirteen water-borne fluoroelastomer compositions were prepared.

Specifically, each recipe was prepared from a fluoroelastomer latex thatincluded 70 percent solids, i.e., 100 parts by weight rubber and 43parts by weight water. The latex was masterbatched with about 14 partsof carbon black filler and about 3.5 parts of water. When a blendedcurative system was employed, the curative system was prepared byblending the respective solutions of curative together and subsequentlyadding the mixture to the composition. The curative system employed ineach recipe is listed in Table I. The ingredients are listed in parts byweight per 100 parts by weight fluoroelastomer (phr).

                                      TABLE I                                     __________________________________________________________________________    Curative System Ingredients (parts by weight)                                 Recipe    1 2 3 4  5 6 7 8  9 10                                                                              11 12                                                                              13                                       __________________________________________________________________________    Ingredient                                                                      Stabilized Siloxane 9.0 7.5 7.5 7.0 5.0 5.0 5.0 5.0 3.5 7.5 10 15 20                                              Non-Stabilized Silane 3.5 3.0 5.0                                            7.0 2.0 3.0 5.0 7.0 1.5 --  -- --        __________________________________________________________________________                                         --                                   

The fluoroelastomer latex that was employed included terpolymers ofvinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene, whichwas obtained from Ausimont under the tradename Tecnoflon TN Latex. Thefiller employed was carbon black that was obtained from Cancarb underthe tradename N991UP. The stabilized siloxane was a diamino-siloxanesold by Sivento under the tradename HYDROSIL® 2776. The non-stabilizedsiloxane was γ-aminopropyltriethoxysilane that was obtained from Siventounder the tradename AMEO. It should be understood that Recipes 10-13 arecomparative recipes. Notably, each comparative recipe includes the sameamine content as one of the other recipes within the scope of thisinvention, i.e., one of Recipes 1-9. Because the same amine content hasbeen presented, a proper comparison can be made where the compositionshave the same crosslinking potential.

Where feasible, a film was prepared from each recipe that was about 10mils thick. As noted in the headings of the following tables, theproperties set forth in Table II derived from films that were preparedthe same day that the curative system was added to the recipe, and thefilm was cured at 100° C. for about one hour; the properties set forthin Table III derived from films that were prepared the same day that thecurative was added to the recipe, and the film was cured for seven daysat room temperature; and, the properties set forth in Table IV derivedfrom films that were prepared ten days after the curative was added tothe recipe, and the film was cured at 100° C. for one hour.

                                      TABLE II                                    __________________________________________________________________________    Film Prepared on Day 1 Cured at 100° C. for 1 Hour                     Recipe     1  2  3  4  5  6  7  8  9  10 11 12 13                             __________________________________________________________________________    Tensile Strength (psi)                                                                   2179                                                                             1541                                                                             1973                                                                             1790                                                                             1414                                                                             1440                                                                             1584                                                                             1488                                                                             1548                                                                             1218                                                                             1054                                                                             1010                                                                             1513                             Elongation at Break (%) 332 415 394 301 203 494 374 263 734 670 527 427                                                    235                              Modulus at 100% (psi) 647 574 753 770 390 455 678 892 300 372 446 656                                                      750                            __________________________________________________________________________

Based on the foregoing data in Table II, it should be evident that theuse of the curative system according to the present invention providesfor cured fluoroelastomer films having improved tensile strength overthose films that simply employ a stabilized amino-siloxane curative. Itshould also be evident, based on the data in Table II, that the modulusat 100 percent, which is indicative of the completeness of the cure, wasimproved for those compositions that employed the curative of thepresent invention.

                                      TABLE III                                   __________________________________________________________________________    Film Prepared on Day 1 Cured at Room Temperature for 7 Days                   Recipe     1  2  3  4  5 6  7  8  9 10                                                                              11                                                                              12                                                                              13                                  __________________________________________________________________________    Tensile Strength (psi)                                                                   850                                                                              910                                                                              868                                                                              1112                                                                             --                                                                              821                                                                              1071                                                                             915                                                                              --                                                                              --                                                                              --                                                                              --                                                                              --                                    Elongation at Break (%) 1000 912 752 609 -- 1073 828 618 -- -- -- -- --       Modulus at 100% (psi) 280 278 329 448 -- 237 293 366 -- -- -- --            __________________________________________________________________________                                              --                              

Table III shows that the properties of a film prepared according to thepresent invention and cured at room temperature for seven days arecomparable to those similar compositions that were cured at 100° C. forabout one hour. The improved usefulness of the curative system of thepresent invention is exemplified by the fact that the non-stabilizedcurative did not cure within seven days at room temperature.

                                      TABLE IV                                    __________________________________________________________________________    Film Prepared after 10 Days Cured at 100° C. for 1 Hour                Recipe     1  2  3  4  5  6  7  8  9  10 11 12 13                             __________________________________________________________________________    Tensile Strength (psi)                                                                   1950                                                                             1493                                                                             1839                                                                             1800                                                                             1420                                                                             1569                                                                             1397                                                                             1430                                                                             1490                                                                             1190                                                                             1080                                                                             1100                                                                             1480                             Elongation at Break (%) 340 421 381 340 210 508 389 291 740 710 518 415                                                    220                              Modulus at 100% (psi) 630 563 749 782 380 471 643 808 310 380 455 660                                                      740                            __________________________________________________________________________

The data of Table IV clearly demonstrates that the cure activity of thecurative system of the present invention is not deleteriously impactedafter about ten days. Indeed, the tensile strength, elongation at break,and modulus at 100 percent are comparable to those similar compositionswherein a film was prepared on the same day that the curative was addedto the latex.

The compositions remaining from above Recipes were stored at roomtemperature and observed on a daily basis until a gelation point wasachieved. Table V sets forth the approximate gelation times for eachrecipe.

                                      TABLE V                                     __________________________________________________________________________    Recipe 1 2  3 4 5 6  7 8 9  10 11 12 13                                       __________________________________________________________________________    Gelation (days)                                                                      30                                                                              30 25                                                                              19                                                                              40                                                                              35 24                                                                              12                                                                              >40                                                                              >40                                                                              >40                                                                              >40                                                                              35                                       __________________________________________________________________________

Based on the foregoing data, it should be evident that the use of thecurative system of the present invention provides for compositions thathave a useful pot life. This is extremely advantageous inasmuch as thewater-borne systems of the prior art have a pot life that is very short.

Still further, those films prepared from Recipes 3 and 13, as well as 9and 10, which were formed on the same day that the curative was added tothe latex, and were cured and tested according to ASTM D-4541 foradhesion strength. Table VI sets forth the adhesion properties for thefluoroelastomer films in conjunction with aluminum, carbon steel, sandblasted stainless steel, and non-sand blasted stainless steel.

                                      TABLE VI                                    __________________________________________________________________________               100° C. for                                                                  100° C. for 1 hour plus                                                           100° C. for                                                                  100° C. for 1 hour plus                Cure Conditions: 1 hour 200° C. for 1 hour 1 hour 200° C.                                       for 1 hour                                  __________________________________________________________________________               Aluminum         Carbon Steel                                      Recipe 10 Adhesion (psi)                                                                 1300  1500       1400  1600                                          Recipe 9 Adhesion (psi) 1350 1450 1400 1580                                   Recipe 13 Adhesion (psi) 1275 1500 1400 1600                                  Recipe 3 Adhesion (psi) 1950 2250 2000 2280                                 __________________________________________________________________________               Stainless Steel                                                               Sandblasted      Not Sandblasted                                   Recipe 10 Adhesion (psi)                                                                 1200  1500        900   890                                          Recipe 9 Adhesion (psi) 1180 1500  850  850                                   Recipe 13 Adhesion (psi) 1150 1480  850  900                                  Recipe 3 Adhesion (psi) 1700 2000 1600 1500                                 __________________________________________________________________________

It should be evident from the data in Table VI that those recipesrepresenting embodiments of the present invention clearly outperformthose that simply employ stabilized amino siloxane as a curative.

EXPERIMENT II

Twelve water-borne fluoroelastomer compositions were prepared.Specifically, each recipe was prepared from a fluoroelastomer latex thatincluded 70 percent solids, i.e., 100 parts by weight rubber and 43parts by weight water. The latex was masterbatched with about 14 partsof carbon black filler and about 3.5 parts of water. When a blendedcurative system was employed, each curative system was prepared byblending the respective aqueous solutions of curative together andsubsequently adding the mixture to the composition. The curative systememployed in each recipe is listed in Table VII. The ingredients arelisted in parts by weight per 100 parts by weight fluoroelastomer.

                                      TABLE VII                                   __________________________________________________________________________    Recipe               1 2 3 4 5 6 7 8 9 10                                                                              11                                                                              12                                 __________________________________________________________________________    Ingredient                                                                      Stabilized Siloxane based on:                                                 (γ-Aminopropyl)triethoxysilane -- -- -- -- -- -- 8.0 -- -- -- --                                                 --                                   N-β-Aminoethyl-γ-aminopropyltrimethoxysilane 7.3 7.3 7.3 --                                                 -- -- -- -- -- -- 7.0 7.0                                                      Trimethoxysilylpropyldiethylen                                               etriamine -- -- -- 8.0 8.0 8.0                                                -- 8.0 8.0 8.0 7.0 --                Non-Stabilized Silane:                                                        (γ-Aminopropyl)triethoxysilane -- -- -- -- -- -- -- 3.0 5.0 7.0                                                  -- --                                N-β-Aminoethyl-γ-aminopropyltrimethoxysilane 3.0 5.0 2.0 3.0                                                7.0 5.0 7.0 -- -- -- -- --                                                     Trimethoxysilylpropyldiethylen                                               etriamine -- -- -- -- -- -- --                                                -- -- -- -- 7.0                    __________________________________________________________________________

The fluoroelastomer latex that was employed included terpolymers ofvinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene, whichwas obtained from Austimont under the tradename Tecnoflon TN Latex. Thefiller employed was carbon black as obtained from Cancarb under thetradename N991UP. The stabilized siloxane was a diamino-siloxane sold bySivento, under the tradename HYDROSIL® 2776. The non-stabilized siloxanewas y-aminopropyltriethoxysilane was also obtained from Sivento underthe tradename AMEO.

Where feasible, a film was prepared from each recipe that was about 10mils thick. As noted in the headings of the following tables, theproperties set forth in Table VIII derived from films that were preparedthe same day that the curative system was added to the recipe, and thefilm was cured at 100° C. for about one hour.

                                      TABLE VIII                                  __________________________________________________________________________    Film Prepared on Day 1 Cured at 100° C. for 1 Hour                     Recipe        1  2  3  4  5  6  7  8  9  10 11 12                             __________________________________________________________________________    Tensile Strength (psi)                                                                      2074                                                                             2969                                                                             3062                                                                             1537                                                                             1912                                                                             1682                                                                             2021                                                                             1404                                                                             1347                                                                             1665                                                                             1213                                                                             1035                             Elongation at Break (%) 389 324 280 395 339 251 281 378 335 265 427 318       Modulus at 100% (psi) 507 883 1060 403 622 831 857 377 545 677 272 532                                                      Adhesion to Carbon Steel                                                     (psi) 1500 1700 1800 1200                                                     1700 1400 2400 1300 1500                                                      1100 1450 1700                 __________________________________________________________________________

Based on the data in Table VIII, it should be evident that the use ofthe curative system according to the present invention provides forcured fluoroelastomer films having improved physical properties. Itshould also be evident, based on the data in Table VII, that theadhesion to a carbon steel was improved as measured by the methoddefined in ASTM D-4541.

Based upon the foregoing disclosure, it should now be apparent that theuse of the novel curative system described herein will carry out theobjects set forth hereinabove. It is, therefore, to be understood thatany variations evident fall within the scope of the claimed inventionand thus, the selection of specific component elements can be determinedwithout departing from the spirit of the invention herein disclosed anddescribed. In particular, fluoroelastomers employed are not necessarilylimited to those exemplified herein. Also, as noted herein, the use of afiller is optional. Thus, the scope of the invention shall include allmodifications and variations that may fall within the scope of theattached claims.

What is claimed is:
 1. A water-borne fluoroelastomer compositioncomprising:an aqueous dispersion of a fluoroelastomer polymer; fromabout 2 to about 30 parts by weight per one hundred parts by weight ofpolymer of a curative system, said curative system having been formed byblending from about 6 to about 94 parts by weight of a stabilizedsiloxane and from about 94 to about 6 parts by weight of anon-stabilized silane, where said stabilized siloxane and saidnon-stabilized silane total about one hundred parts by weight of thecurative system; from 0 to about 40 parts by weight of an additivefiller per one hundred parts by weight of polymer; and sufficient waterto provide a composition having a solids content of from about 10 toabout 80 percent by weight of the total composition.
 2. A water-bornefluoroelastomer composition, as set forth in claim 1, wherein saidfluoroelastomer polymer is a copolymer of vinylidene fluoride andhexafluoropropylene, a terpolymer of vinylidene fluoride,hexafluoropropylene and tetrafluoroethylene, or a mixture thereof.
 3. Awater-borne fluoroelastomer composition, as set forth in claim 1, wheresaid curative system has been formed by preblending said stabilizedsiloxane and said non-stabilized silane prior to their addition to thecomposition.
 4. A water-borne fluoroelastomer composition, as set forthin claim 1, wherein said non-stabilized silane is selected fromcompounds defined by the formula III ##STR4## where R⁶ is an aminogroup, and R⁷, R⁸, and R⁹ are independently selected from hydroxylgroups, hydrogen atoms, halogen atoms, amino groups, and organicmoieties.
 5. A water-borne fluoroelastomer composition, as set forth inclaim 1, wherein said non-stabilized silane isγ-aminopropyltriethoxysilane,N-β-aminoethyl-γ-aminopropyltrimethoxysilane, ortrimethoxysilylpropyldiethylenetriamine.
 6. A water-bornefluoroelastomer composition, as set forth in claim 1, wherein saidstabilized siloxane is an oligomer having an average degree ofpolymerization that is essentially limited to a trimer.
 7. A water-bornefluoroelastomer composition, as set forth in claim 6, wherein saidstabilized siloxane is selected from compounds defined by the formula I##STR5## wherein R¹, R², and R³ are the same or different and areselected from the group consisting of amino groups, organic moieties andhydrogen, with the proviso that at least one of R¹, R² and R³ contain anamino group.
 8. A water-borne fluoroelastomer coating composition, asset forth in claim 7, wherein at least two of R¹, R² and R³ containamino groups or at least one of R¹, R² and R³ contain a polyamino group.9. A water-borne fluoroelastomer coating composition, as set forth inclaim 7, wherein at least one of R¹, R² and R³ are defined by theformula (II) ##STR6## wherein R⁴ is a divalent organic moiety, R⁵ is ahydrogen atom, an organic moiety, or an amino group, and n is 0 or 1.10. A water-borne fluoroelastomer coating composition, as set forth inclaim 1, wherein said filler is carbon black, mineral fillers, clays,synthetic silicates, whiting, barytes, color pigments, glass microbeads, short, chopped fibers, metal powders, graphite or mixturesthereof.
 11. A water-borne fluoroelastomer coating composition, as setforth in claim 1, wherein said additive filler comprises materials tomodify resistivity.
 12. A water-borne fluoroelastomer compositioncomprising:an aqueous dispersion of a fluoroelastomer polymer; fromabout 2 to about 30 parts by weight per one hundred parts by weight ofpolymer of a curative system, said curative system comprising a mixtureof a stabilized siloxane and non-stabilized silane; from 0 to about 40parts by weight of an additive filler per one hundred parts by weight ofpolymer; and sufficient water to provide a composition having a solidscontent of from about 10 to about 80 percent by weight of the totalcomposition.